Holding a connection in an ISDN network with a DECT intermediate system

ABSTRACT

In a method for operating a connection in an ISDN network (NE) by integrating at least one DECT intermediate system (IS) in which, from the protocol of the connections, the triplet (terminal address (TE  1 )/call identification (CR  2 )/identifier of the transmission service (BC  1 )) for each connection is stored in a list in the DECT intermediate system, it is provided that, upon the arrival of the confirmation (HOLD ACK) for the holding of a connection, this triplet (TEI  1 /CR  2 /BC  1 ) is marked; upon the arrival of a confirmation (RETR ACK) of the reactivation of a connection under the same terminal address (TEI  1 ), the marked call identification (CR  2 ) is searched for in the list; and then a DECT connection is made available, which connection corresponds to the identifier of the transmission service (BC  1 ) of the marked triplet (TE  1 /CR  2 /BC  1 ), and finally the marker (X) is erased again.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for operating a connection inan ISDN network by integrating at least one intermediate system in whichconnections are led between subscribers of the ISDN network, whereby theprotocols contain a terminal address, a caller identification and anidentifier of the transmission service, among other things, the terminaladdress, caller identity and identifier of the transmitting service fromthe protocol being stored in a list in the intermediate system for eachconnection.

In the same way, the invention relates to an intermediate system whichis integrated into an ISDN network, wherein connections are led betweensubscribers of the ISDN network via the intermediate system, and whereina list is provided in the intermediate system for purposes of storingthe terminal address, the caller identification and the identifier ofthe transmission service from the protocol for each connection.

2. Description of the Related Art

The ISDN communication system (Integrated Services Digital Network) isdistinguished, among other ways, in that a number of auxiliary servicescan be made available by the network operator, the holding ofconnections being the service of interest here. In this auxiliaryservice, an existing connection can be shifted into hold mode by asubscriber and reactivated later.

The channel structure in ISDN comprises two useful channels called Bchannels, each with 64 kpbs, as well as one control channel, called Dchannel, with 16 kbps. The B channels serve for the transmission ofuseful information, namely data, voice or 3.1 kHz audio, whereas the Dchannel transmits control information. At a base terminal, called theS_(o) interface, up to eight terminal devices can be connected; aconnection can exist via each B channel, that is, two connectionssimultaneously per base terminal. The ISDN system provides threeprotocol layers, layer 3 serving for purposes of connection control(connection setup and dismantling by means of call identification andidentification of the transmission service, controlling of auxiliaryservices), layer 2 serving for terminal addressing, securingtransmission, etc., and layer 1 serving for the physical transmission ofall information in the B/D channels via the extension circuit.

The DECT (Digital Enhanced Cordless Telecommunications) standard wascreated for wireless communication over short distances and is usedprimarily for cordless telephones, or respectively, facilities.Basically, a radio connection is set up between a stationary part, whichis connected to the stationary network, and one or more mobile parts, auseful channel with 32 kbps and a control channel with 2 kpbs usuallybeing provided. DECT connections can also be utilized in a stationarymanner between an interface of an ISDN network and the S_(o) interfaceat the subscriber side, particularly when a cable connection cannot beinstalled for structural reasons or would be more expensive than theradio connection.

It is thus desirable to produce, or respectively, to maintain an ISDNconnection with an intermediately connected DECT connection, whilelimiting the performance features present in the ISDN system as littleas possible. The invention is particularly concerned with the problem ofmaking available the ISDN auxiliary service “hold (connections)” whenthe connection is running via a DECT intermediate system (or severalDECT intermediate systems). The ISDN protocol for “hold” does notcontain the parameters for identifying the transmission service in itsdata packets, this parameter being unnecessary, since the B channelstructure in the ISDN system (64 kbps) supports all services.

The intermediate connecting of a DECT system would only enable thischannel transparency if the DECT system was also based on a 64 kbpschannel structure. But this is ruled out by the channel economy requiredin the DECT system.

SUMMARY OF THE INVENTION

It is thus an object of the invention to guarantee the auxiliary service“hold” in an ISDN network even given the integrating of one or moreintermediate systems, meaning primarily DECT intermediate systems,though it should also be possible to integrate other systems, be theywirebound or wireless.

This object is inventively achieved in a method of the type cited abovein that, upon the arrival of the confirmation for holding a connection,the triplet (terminal address/call identification/identification of thetransmission service) is marked; upon the arrival of a confirmation ofthe reactivation of a connection under the same terminal address, themarked call identification is searched for in the list, and a connectionof the intermediate system which corresponds to the identification ofthe transmission service of the marked triplet is made available; andfinally, the mark is erased.

The invention guarantees that in the restoring of a held connection, theintermediate system recovers the appertaining transmission service via acomparison of the stored and marked parameters.

It is expedient when the intermediate system is a DECT intermediatesystem and when connections between subscribers of the ISDN network areled via a first DECT station, an air radio link, and a second DECTstation.

It is advantageous if, in the holding of a connection in thetransmission service “unlimited digital information”, the correspondingbandwidth is also held available for voice connections, and amodification onto half bandwidth is prevented.

It may also be expedient when a DECT channel that is already availableis allocated to the connection that is to be reactivated, orrespectively, when a new and appropriate DECT channel is selected forthe connection that is to be switched back.

An intermediate system of the above described type is inventivelycharacterized for purposes of achieving the inventive object in that theintermediate system and the list are designed to provide the triplet(terminal address/call identification/identification) of thetransmission service with a mark upon the arrival of the confirmationfor holding a connection, to search out the marked call identificationin the list upon the arrival of a confirmation of a reactivation of aconnection under the same terminal address, to make available aconnection of the intermediate system which corresponds to theidentification of the transmission service of the marked triplet, and toerase the mark.

It is advantageous here when the intermediate system is a DECTintermediate system, whereby the connections between subscribers of theISDN network are led via a first DECT station, an air radio link, and asecond DECT station, and a DECT station, and when a DECT station and thelist are designed to provide the triplet (terminal address/callidentification/identification) of the transmission service with a markupon the arrival of the confirmation for holding a connection, to searchout the marked call identification in the list upon the arrival of aconfirmation of a reactivation of a connection under the same terminaladdress, to make available a DECT connection which corresponds to theidentification of the transmission service of the marked triplet, and toerase the mark.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and all of its advantages are detailed below withreference to the drawing, in which appear:

In FIG. 1 is a symbolic block circuit diagram of a telecommunicationnetwork with an ISDN system and an intermediately connected DECT system;in

FIG. 2 is a block circuit diagram of a DECT intermediate system asdepicted in FIG. 1 and

FIG. 3 is a schematic illustration showing the exchange of the hold andswitch-back messages and the entering into a list of the DECTintermediate system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 demonstrates that an ISDN network NE is connected via a DECTintermediate system IS to a plurality of endpoints TE A, TE B, TE C,which share an interface S_(o) in the ISDN standard. Here, the DECTintermediate system IS consists of a stationary part, generally a firstDECT station FP, and a mobile part, generally a second DECT station PP,it being possible to set up an air radio link CI between the twostations. Various interfaces, referenced IF here, can be present betweenthe ISDN network NE and the DECT intermediate system IS. Two subscribersTE1, TE2 are depicted as being connected to the network NE.

Referring to FIG. 2, it is clear that both the first and second stationsFP, or respectively, PP of the DECT intermediate system comprise aworking unit FIWU, or respectively, PIWU. In order to be able tocorrespondingly control the internal DECT functions, the intermediatesystem IS must have enough information about the current ISDN protocols.In the following and in FIG. 2, the protocol layers in ISDN, orrespectively, in the DECT system are referenced I-L1, I-L2 and I-L3, orrespectively, D-L1, D-L2, and D-L3. Details about the ISDN system, orrespectively, the DECT system, and particularly about the protocolstructure in these systems, can be derived from the followingliterature: ETSI Standards ETS 300 175 and ETS 300 196 as well as ITUrecommendations 1.411, Q.921 and Q.931.

In addition to what has already been stated about the protocol layers,it should be noted in the context of the present invention that the ISDNprotocol layers L1 and L2 terminate in the stationary and mobile partsFP, PP, and the ISDN protocol layer L3 is extended through theintermediate system basically transparently, the ISDN-L3 packets being“packed” into DECT-L3 packets.

In order to obtain the above information, the DECT intermediate systemIS contains an I-L3 monitor function, which is contained in the workingunit FIWU of the stationary part FP as block L3-MON in this case andwhich analyzes the protocol of the ISDN-layer 3 and stores essentialparameters for every call. For controlling the DECT system, the workingunit FIWU of the stationary part FP has a master function, as opposed tothe working unit PIWU of the mobile part PP, which only has a slavefunction, whereby the working unit FIWU of the stationary part FPcontrols that of the mobile part PP via D-L3 protocol elements.

The following describes the setup of a connection between the ISBNnetwork NE via the DECT intermediate system IS and an ISDN system, orrespectively, a subscriber (interface So), with reference to FIG. 3.

When the calling subscriber TE A with the terminal identifier, forinstance TEI A (subscriber A), picks up at his terminal, the terminalsends a setup message (set up) in the direction of the network. In thissetup message, a call identification, for instance CR2, is defined, andthe identifier of the transmission service (bearer capabilities) BC isindicated, thus communicating to the network which transmission serviceis required, for instance the service “voice”. In the intermediatelyplaced DECT system IS, the setup message is analyzed, namely by theworking unit FIWU in the stationary part FP, whereby it is determinedthat a subscriber is calling which has the call identification CR2 andthe identifier of the transmission service “voice”. This tripletTE1-CR2-BC1 is stored in a memory, or respectively, in a list LIS and,according to the specifications, a DECT connection is set up which issuited to transmit voice. The ISDN network that receives this setupmessage now determines that someone desires a connection. But there isno information available to the network to the effect that a DECT systemis intermediately connected.

As in an analog network, the ISDN network now overlays a dial tone andacknowledges the setup message. Accordingly, the network delivers amessage “setup confirmation” and requests the subscriber A and theterminal to give dialing information. The DECT system sends through thissetup message, which also contains an item of information about the Bchannel on which this connection is to be based, without modification.The subscriber now inputs the dialing information to the network, whichreceives the call number. The DECT system sends the correspondinginformation packet through transparently. Once the network recognizesthe dialed number as usable, it delivers what is known as a “callproceed” message to subscriber A.

The called subscriber TE1 is now reached, and it rings there, at whichpoint the has not yet picked up. The subscriber reports this in ISDNprotocol level 3 to the network. When the network has established this,it delivers an alert signal (“alerting message”) to the callingsubscriber TE A. In voice service, this is always accompanied by thecorresponding signals in the useful channel. Eventually, the calledsubscriber TE1 then picks up, and a connected-signal (“connect”) isdelivered to the calling subscriber TE A; that is, the called subscriberTE 1 is connected, and the call is now in the active state (conversationstate) at the called subscriber TE 1.

The setup message goes to the network on the called side. When thenetwork has sufficient dialing information, the network sends a setupmessage on the calling side to the desired called subscriber. In thismessage, the network communicates a call identification and theidentifier of the transmission service, which is of course the same ason the calling side. The network merely produces the relation to thecall identifications, which are present as a very specific bit patternat a specific point in the protocol.

Since it is possible in an ISDN network to maintain a plurality ofseparately signaled connections simultaneously, whereby the signalingprocesses can be superimposed on one another, a call identification isneeded in each signaling process, along with a process numbering, whichit is possible to assign basically arbitrarily, in order to be able totell the signaling processes apart. In principle, this callidentification is always specified by the one making the call; that is,the subscriber can assign it to the network or vice versa, and allothers then refer thereto.

The call identifications are not identical between the calling andcalled sides, since they are specified locally. The network makes surethat the calls are adapted to each other and delivers a setup messagewith a call identification and with the desired identifier of thetransmission service on the called side as well.

In the ISDN system, up to eight terminal devices can be connected to abase terminal. When all eight terminal devices are compatible with thecall, all would check in; that is, all of them would deliver a servicesignal (“alert”). In fact, the terminal device that picks up first andsends “connected”, accordingly, gets the call. It is also possible forseveral service signals and several “connected” signals to run inparallel; what is crucial is that the terminal device that picks upfirst receives the call. The network subsequently determines whichterminal gets the call by a connection confirmation (“connectionacknowledge”), which is sent to the terminal device that receives thecall. This is unambiguously defined by the terminal identifier, sinceeach terminal device has a different terminal identifier. The terminaldevice thus has its service signal and/or its “connected” message alwaysprovided with an individual terminal identifier. The first device tocheck in is thus unambiguously identifiable, and the connectionconfirmation is delivered to it, whereby all these messages always havethe same call identification, since they always refer to the same call.Subsequent to the connection confirmation, the connection is also activeat the called subscriber, and the subscribers can communicate with eachother.

It should be noted at this point that, in contrast to the illustrationaccording to FIG. 1, a DECT intermediate system may also be present onthe called side (here subscriber TE1), at which the triplet TEO-CR-BC islikewise stored in a list.

In a call in the active state, the auxiliary service “hold” can be used.In the course of a conversation of the two subscribers, one subscribercould want to consult another subscriber, for example. The subscriberscan arrange this, and one subscriber, for instance TE A, then activatesa hold or consult button on his side, which causes the previouslyexisting connection to be switched into hold. This is signaled to theother subscriber TE 1 unambiguously; the connection remains, and thecharges accrue to the caller.

The subscriber TE A, which switches to hold, would like to activate afollow-up call and needs a B channel for this purpose. The ISDN systemreserves a B channel for this purpose, because otherwise one of theother terminal devices, if there are others connected, could “take away”this channel from the subscriber TE A, who has just switched into hold.

The corresponding explanation of this process follows, with particularreference to FIG. 3. If the subscriber TE A wishes to switch hisconnection to hold, a hold message HOLD is delivered by his terminal(FIG. 3, top), whereby it is assumed in this example that this holdmessage HOLD is delivered to the call identification 2.

In the working unit FIWU of the stationary part FP, there is a list LIS,that is, a memory. In this example, it is assumed that severalconnections run from the interface So in the direction of the networkNE. Of these the call identification 2 is newly active for TEI 1. Thehold message is now sent thereto; the DECT intermediate system IStransfers it to the stationary part FP, which can examine the message,though it does not need to at the moment. In any case, it forwards thehold message to the network NE, which now executes the correspondingcontrol functions and acknowledges the message positively with a holdconfirmation HOLD ACK. The stationary part FP now determines that thecall identification 2 is held and marks this call identification 2 inits list LIS under the terminal address TEI1 (network side) with an Xmarker. The hold confirmation HOLD ACK travels to the subscriber TE 1via the DECT intermediate system. It may also be the case that the call,or respectively, the function, is rejected, because the performancefeature is not functioning, etc. In this case, a hold rejection wouldarrive instead of a hold confirmation, and the connection would not goto hold.

The information is now present in the DECT information system IS that aconnection with the identifier of the transmission service 1 is on hold,and it must make sure that the corresponding identifier of thetransmission service is reconstructed when this connection is neededagain. The DECT intermediate system IS can hold the connection. It wouldalso be possible to set up a new connection for every follow-up call andto allocate a new DECT channel. However, it is usually more expedient tohold the DECT connection already in existence, to wait for the follow-upcall and to check if this still has the same identifier of thetransmission service or if it has a different one. If the sameidentifier of the transmission service is present, the DECT channel canbe used again; if another is present, the channel must be modified, oranother channel set up. In most cases, the identifier of thetransmission service does not change, though a change is not out of thequestion.

If a voice call were to be made, then the connection were to be put onhold, and finally a PC (computer) were to be called as a thirdsubscriber (e.g. under TE 1, CR 1, BC 3), one would have a dataconnection which does not present a problem in the ISDN system, sinceits B channel can support both, namely voice or data connection.However, the DECT intermediate system would now determine that the heldchannel is suited to the voice connection, but not to the dataconnection. In this case, a channel for the data connection can be setup, and the channel for the voice connection can be dismantled. But theconnection as a whole is held.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

The lower part of FIG. 3 now relates to the case in which the subscriberTE A has completed his consultation and would like to reactivate theoriginal connection. A switch-back message RETR (“RETRIEVE”) is thensent from the terminal TE A to the network at the call identification CR2. In the example illustrated in FIG. 3, for TEI 1 a connection was alsoheld under the call identification 3 in the list; that is, it would alsobe possible to switch back to the call “no. 3”. In any case, it iscritical that the intended call identification is inserted into theswitch-back. This message travels through the DECT intermediate systemIS to the network again; the network confirms or rejects thisswitch-back message; and the normal case of a confirmation withswitch-back confirmation RETR ACK is present at the call identification2. This is the signal for the DECT intermediate system IS to set up aconnection that corresponds to the identifier of the transmissionservice 1 that is connected to the call identification 2. It is alsopossible that an entirely different identifier of the transmissionservice has meanwhile appeared, though the one belonging to the originalcall must be reconstructed, for which purpose the X in the list LIS isused, since the identifier of the transmission service is not containedin the switch-back message.

The three most important actions can be summarized as follows:recognizing the switch-back message at the terminal identifier TEI 1;searching in the list LIS for the call identification 2; makingavailable the appropriate identifier of the transmission service, hereBC 1, as the basis for the DECT connection. The connection is then setup again, and the mark X is erased. If a subscriber should now switchinto hold again, the described sequence would repeat.

The invention has been described in connection with a DECT intermediatesystem; however, it should be clear that other cordless systems alsocome under consideration, such as cable-bound intermediate systems,etc., for instance with IR transmission paths. Of course, such anintermediate system is predicated on the channel structure notconflicting with the ISDN channel structure, or respectively, on theability to set up corresponding channel structure during the connectioncontrol.

I claim:
 1. A method for operating a connection in an ISDN network byintegrating at least one intermediate system, in which connections areled between subscribers of the ISDN network, protocols contain aterminal address, a call identification and an identifier of thetransmission service and from the protocol, the terminal address, thecall identification and the identifier of a transmission service foreach connection are stored in a list, comprising the steps of: upon thearrival of a confirmation for holding of a connection, marking a tripletterminal address/call identification/identifier of the transmissionservice is, upon the arrival of a confirmation of a reactivation of aconnection under a same one of said triplet terminal address, searchingfor a marked call identification in the list, making available aconnection of the at least one intermediate system, said connectioncorresponding to the identifier of the transmission service of themarked triplet terminal address, and erasing the marker.
 2. A method asclaimed in claim 1, wherein the intermediate system is a DECTintermediate system, and further comprising the step of: leadingconnections between subscribers of the ISDN network via a first DECTstation, an air radio link and a second DECT station.
 3. A method asclaimed in claim 2, further comprising the steps of: given holding of aconnection in the transmission service “unlimited digital information”,keeping the corresponding bandwidth for voice connections available, andpreventing a modification onto half bandwidth.
 4. A method as claimed inclaim 2, further comprising the step of: allocating a DECT channel thatis already available to the connection that is switching back.
 5. Amethod as claimed in claim 2, further comprising the step of: selectinga new and suitable DECT channel for the connection that is switchingback.
 6. An intermediate system which is integrated in an ISDN network,comprising: connections between subscribers of the ISDN network led viathe intermediate system, and a list in the intermediate system forstoring a terminal address, a call identification, and an identifier ofthe transmission service for each connection from a protocol, theintermediate system and the list being designed to provide the tripletterminal address/call identification/identifier of the transmissionservice with a marker upon arrival of a confirmation for holding aconnection, to search for a marked call identification in the list givenarrival of a confirmation of a reactivation of a connection under thesame terminal address, to make available a connection of theintermediate system which corresponds to an identifier of thetransmission service of the marked triplet, and to erase the markeragain.
 7. An intermediate system as claimed in claim 6, comprising: aDECT intermediate system in which connections between subscribers of theISDN network are led via a first DECT station, an air radio link and asecond DECT station, and in which one of said DECT station and the listare designed to provide the triplet terminal address/callidentification/identifier of the transmission service with a marker uponthe arrival of the confirmation for holding a connection, to search forthe marked call identification in the list upon the arrival of aconfirmation of a reactivation of a connection under the same terminaladdress, to make available a DECT connection of the intermediate systemwhich corresponds to the identifier of the transmission service of themarked triplet, and to erase the marker again.